New methods for stereoselective formation of carbon-carbon bonds at ring junctions of polycyclic molecules are of value in the construction of complex molecules. This proposal describes a new version of the Claisen rearrangement which attaches, in high yield, an allyl group to a ring junction. A detailed study of this reaction in several polycyclic systems proposed, the major goal of which is the determination of the factors which control its stereochemical outcome. Finally, schemes for utilizing this new reaction are proposed for the total synthesis of the potent anti-viral agent aphidicolin, the plant growth hormone gibberellic acid and the novel sequiterpene prezizaene.